1. Field of the Invention
This invention relates to electronic oscillators. More specifically, this invention relates to low-phase noise oscillators utilized in sensitive radar systems and the like.
While the present invention is described herein with reference to a particular embodiment, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional embodiments within the scope thereof.
2. Description of the Related Art
Sophisticated radar and communications schemes often require the detection of relatively faint or noise-obscured signals. As a result, advanced radar systems have become extremely sensitive to detect signals reflected by small targets and by targets operating in adverse environmental conditions.
Such advanced systems typically include a wide dynamic range receiver and a low phase noise frequency reference unit. Of central importance to the sensitivity of such systems is the capability of the frequency reference unit to generate or synthesize a highly stable designated frequency. A highly stable (low phase noise) frequency corresponds to one in which substantially all signal energy is confined to an extremely low spectrum deviation.
Many widely-used frequency reference units incorporate one of a variety of conventional oscillator circuits. Among the oscillator networks most frequently employed are those commonly known as Pierce, Colpitts, Clapp and Butler oscillators. Unfortunately, it is anticipated that future high frequency radar designs will require oscillators having a lower phase noise than that exhibited by the conventional networks enumerated above. For example, conventional oscillators are generally characterized by phase noise in excess of -160 dBc/Hz at a 20 kHz offset from oscillation frequencies (f.sub.0) exceeding 100 MHz. In contrast, future high frequency coherent radar designs may be expected to impose noise requirements of better than -170 dBc/Hz at a 20 kHz frequency offset.
Conventional oscillators may also be characterized as either balanced or unbalanced. In balanced configurations, signals within the oscillator combine so as to reduce the amplitude level of the even harmonics and offer better noise performance thereof.
Accordingly, a need in the art exists for a low phase noise balanced oscillator disposed to initiate oscillation without the aid of external circuitry.